In a typical prior art magnetic disk recording system a slider containing magnetic transducers for reading and writing magnetic transitions flies above the disk while it is being rotated by a spindle motor. The disk includes a plurality of thin films and at least one ferromagnetic thin film in which the recording (write) head records the magnetic transitions in which information is encoded. The magnetic domains in the media on can be written longitudinally or perpendicularly. The read and write head portions of the slider are built-up in layers using thin film processing techniques. Typically the read head is formed first, but the write head can also be fabricated first. The conventional write head is inductive.
In a disk drive using perpendicular recording the recording head is designed to direct magnetic flux through the recording layer in a direction which is generally perpendicular to the plane of the disk. Typically the disk for perpendicular recording has a hard magnetic recording layer and a magnetically soft underlayer. During recording operations using a single-pole type head, magnetic flux is directed from the main pole-of the recording head perpendicularly through the hard magnetic recording layer, then into the plane of the soft underlayer and back to the return pole in the recording head. The shape and size of the main pole and any shields are the primary factors in determining the track width.
In U.S. Pat. No. RE33,949 to Mallary, et al. a head for perpendicular recording is described which includes a “downstream shield” which is separated from the write pole by a small gap. The arrangement is said to intercept most of the downstream fringing flux by the flux return section so that the flux return section acts as a magnetic shield. The interception of the downstream fringing flux by the magnetic shield reduces the undesirable effect of reversing, or weakening, a previously recorded bit of information. The air-bearing surface (ABS) face of the shield is designed to be many times as large as the face of the main (write) pole piece so that the density of the flux from the main pole tip is sufficient to effect a vertical recording while the density of the flux passing into the downstream magnetic shield is low and a previously recorded pattern is not reversed.
FIG. 1 illustrates a prior art head 26 for perpendicular recording and the associated media 27. The head is described in an article by M. Mallary, A. Torobi and M. Benakli published in IEEE Transactions on Magnetics, vol. 38, no.4, July 2002. The head 26 has a trailing shield pole 33 and side shields (not shown). The magnetoresistive sensor 35 is flanked by shields 36, 37. This head is workable with a leading magnetoresistive head structure because two pancake coils 35A, 35B are used to ensure that the read head shield 36 is at the same magnetomotive potential as the trailing shield pole 33 and the soft underlayer 29 of the medium 27. The flux paths are illustrated by lines 39 which show the write pole originating the flux at the ABS which then is divided between the trailing shield pole 33 and the read head shield 36 after passing through the hard ferromagnetic recording layer 28. A disadvantage of this design is that it requires two pancake coils. It also requires a relatively thick return pole which will have to be made of high moment material for the desirable high write field capability, and a very narrow throat height for that element. The figure also shows this design will result in write disturbance of the read shields.
A perpendicular recording head with side shields is discussed in “Numerical Analysis of Narrow-track Single-pole-type Head with side Shields for 1 Tb/in2 recording”; by Kanai, Mohammed, Matsubara, Muraoka and Nakamura; J. Applied Physics; vol. 93, no. 10; May 15, 2003. The two side shields each begin at the ABS and extend a small distance (less than the throat height) into the head. The authors report that finite element modeling of a head with the side shields showed a significant improvement by reducing the off-track field which would allow a narrower track to be written. In a top view, perpendicular to the ABS, the shields taper as they get closer to the main pole piece. Alternatively stated, the side shields are thicker the further they are from the center of the track. The purpose of the tapered shields is to increase the on-track field strength over what was obtained with a constant shield cross-section.
Perpendicular magnetic recording is considered to be superior to longitudinal magnetic recording for ultra-high density magnetic recording. The increase demand for higher areal density has correspondingly led to increase demand to explore ways to reduce the width of the write pole piece, increase the write field strength, and improve the write field gradient. Experimental evidence and modeling have shown that a trailing shield single pole writer (SPT) design achieves a 4–5 dB media signal to noise advantage over writing with the trailing edge of an unshielded pole, increase in dHy/dx of the head field, reduce partial erasure, and improve saturation. These features improve transition sharpness (linear resolution) and permit higher coercive field media (improved stability).